Recirculated exhaust gas (“EGR”) is becoming an important element for both diesel and gasoline engines, particularly engines utilizing charge air boosting or compression (ex. exhaust driven turbocharger or engine driven supercharger,) for both fuel consumption improvements and for the reduction of regulated tailpipe exhaust gas emissions.
In some engine applications two EGR supplies, one high pressure and one low pressure, are supplied to the engine based on the then current engine operating conditions. In engines utilizing an exhaust driven turbocharger, high pressure EGR is typically diverted from a location upstream of the turbocharger and is supplied to the compressed intake charge during high load operation while low pressure EGR is diverted from a location downstream of the turbocharger and is supplied to a location downstream of the throttle body during low load operation. Diverting EGR from a location upstream of the exhaust driven turbocharger may, however, compromise the performance of the turbocharger by limiting the exhaust gas, and resultant exhaust energy available thereto.